Conf42 JavaScript 2021 - Online

Destructuring frontend monoliths with Microfrontends

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In the modern app architecture, the frontend contributes a major chunk of the setup, most of the business logic is housed in the Frontend. Over time the frontend app becomes a huge monolith, harder to maintain, tricker to add new features, etc. With Microfrontends we break this monolith into smaller independent apps. These apps are developed independently but stitched as a SPA on the fly with all the goodies of client-side javascript. This has been done traditionally with several approaches, but with webpack 5 we now have module federation, which opens the door for seamless Microfrontend integrations.

In this talk, we will discuss the complete Microfrontends architecture pattern, how to destructure an existing monolith into Microfrontends with help of module federation from webpack 5. By the end of this talk, the attendees will be having a new vision of how they architect their frontends.


  • Trishul: Today I'll be talking about destructuring front end monolith with micro frontends. Micro frontend architecture is a design pattern where a monolithic frontend app is destructure into small independent apps. This whole microfrontend architecture enables parallel development cycle.
  • Communication between micro frontend and Appshell has been set up. We also use custom events for communicating between one microfrontend ten to another. With webpack five we have module Federation. This allows webpack to reference some modules which are not present at the compile time.
  • Model federation plugin accepts a remote remote one at the address localhost 3002. And it exposes some shared libraries like React and React dome. It's seamlessly forwarding the state from host app to the shared component. With this we have lots of power from module Federation.
  • We have implemented microfrontend and investing in in our shop. The biggest challenge was keeping design consistent throughout all the micro front ends. Instead of doing it manually for every micro frontend, what we use is a templating engine. Another challenge was decoupling code from app shell.
  • Westwing broke its huge monolith into small micro front ends and app shell. Instead of copying this logic into every micro front end, we created small utility NPM packages. This helped us to have a smooth and more productive developer experience.


This transcript was autogenerated. To make changes, submit a PR.
Hello everyone, I'm Trishul. I'm a frontend developer and a JavaScript enthusiast. By day I architect some e commerce solution for Westwing and by night I'm a Mozilla enthusiast. So today I'll be talking about destructuring front end monolith with micro frontends. So what is a monolith? By definition, monolithic application is designed to be a self contained complete of programs are interconnected and interdependent. So monoliths application are self contained applications, the component of which are tightly coupled to each other, interdependent and interconnected components like UI elements, database, everything goes together. In modern day this monolith has already been broken into backend and the frontend, and eventually backend has been broken into microservices. This worked fine for along, but with evolution of JavaScript we have lots of code now in front end. Frontend hosts major chunks of business logic. With lots of code comes lots of complete and now what we have is again called a front end monolith. And with this we have all the problems of monolith again all the code is in a single place, increasing size of repo every day. Every feature we add increases the size of the code and eventually it increases the complexity of the code. Since lots of team are working together on the same code, we have increased interteam dependencies and as a result of all of this our development to deploy cycle has been slowed down. Moreover, the whole team is as strong has the weakest link. If any team has broken anything on the production, all these teams are blocked. No one can deploy anything else until this thing is fixed by the team. So what is our solution? Enters micro front ends? What is a micro frontend? By definition, micro frontend architecture is a design pattern where a monolithic frontend app is destructure into small independent apps. These micro apps are stitched together as a single page on the fly. Consider your huge monolithic system. It has been broken into small, let's say components, and each component behaves on its own. So each macro frontend is a standalone system capable of running on its own. Each macro frontend has an independent repository, a separate piece of code, so that the complexity of its code is contained into this individual repository. It has independent CI pipelines, so you can have your own testing suits, you can have your own deployment pipelines, you can have your own regression pipelines whatsoever. This do not bother other teams. And finally which I love the most, they have independent deployments. Each micro frontend is deployed individually. One team do not have to wait for the other team or is not blocked by the other team. If your code is ready, it's tested. You can already deploy and make sure your live site has the live code as a whole. This whole microfrontend architecture enables parallel development cycle so that every team has their own domain and they can move with their own velocity. Let's have a look at the architecture. So consider this case. There are several micro frontend ends, remote one, remote two, remote three, and a host. So these micro front ends expose these packages in the wild and host consumes those packages. Host does not have to worry about how these were built, how these were compiled or how these were made available. All it needs a remote address where it can get these remotes from. Now let's have a look how we architected our e commerce website at westwing. So at Westwing we have this very simplistic destructure. There's a header, there's a footer, and there are several pages, let's say homepage, product listing page, product detail page, payments, page and cart page, and many more. So in a monolithic word, all these code were in the same code base. All the teams were working on the same code. And obviously there will be lots of friction, lot of to and fro, and most importantly there were lots of blockage because of one team. The other teams have to wait for the deploy. We have to sync our deploy, but with micro front ends, we made every page into a micro frontend, individual from each other and independent. And these micro front ends were consumed by the host. The host has the header and the footer, we generally call it as an app shell. So when a request is made to a page, let's say for the home page, the app shell takes the request and renders the header and the footer with homepage micro frontend. So what should appshell have apart from header and footer? So what we put in app shell is more of shared business logic, which will be kind of consistent throughout all the micro front ends. So one of such logic is login logic. So all the login mechanism we put in app shell if user needs to log in. So instead of micro frontend initiating the logic process, login process, it sends a signal to Appshell and app shell initiates the login process. If the user is logged in, Appshell returns the data of the logged in user, else it shows a login pop up or whatsoever is the logic. But this is consistent in the app shell. And micro frontends do not have to worry about it, they just send the signal and get the response. The next thing which we put here was tracking. So our ecommerce site have different third party tracking, which is common throughout the system. So instead of putting it in each micro frontend, we put it in Appshell, so that it's uniformly available throughout microfrontend ecosystem. So if any micro frontend needs to send a signal, they send a signal to Appshell and Appshell eventually sends it to the third party. This makes sure that we maintain the consistency of tracking, and we have a single place where we can monitor what tracking is being done if we want to log it, if we want to debug it. So it comes really handy. Next thing we put there was system config. So we use lots of config, like the environment config, these pipeline config and whatnot. So instead of putting it in all the micro frontend, we just put it in appshell. And then when any micro frontend needs some of it, they just request from App shell. So app shell basically holds the single source of truth for all the configs throughout the system. Whosoever Microsoft frontend want some configs, they just request it from Appshell and get all of it. And then the final thing which we put in Appshell is these routing. So Appshell is responsible for building all the pages because it has the header and the footer. So we put all the routing logic within the app shell. So for example, if you make a request for a listing page. So existing micro frontend is invoked by the app shell and it is rendered with the header and footer. And finally the complete page is served to the user. So these are some shared business logic, which we put in Appshell called, maybe you can call it host. So we have been talking about lots of data transfer between micro frontend and app shell. So we need to understand how the communication between micro frontend and Appshell has been set up. So there are generally two ways. So in microfrontend ecosystem, if we are using the same tech stack, let's say micro frontends are in react and Appshell is also in react. So the communication is a very easy process. We can just share the props like any react component except the props, and it behaves. Props can be a data or props can be a function. So if you want to change the property of the parent, you can pass some function and eventually the child component will change some property in the parent. Simple react flow. So this shared component is still a react component. So it will still behave how the react behaves. So there is nothing extra layer which we need to do. And the other way is if we have, let's say view js or react or angular, let's say basically some different text stack, not the same text stack throughout ecosystem, then we use something called as custom dome events. So what are custom dome events? So custom dome events are just user generated events. This behave exactly like any other events of the Javascript, but it's just we can create our own in our west Wing system. We also use custom events for communicating between one microfrontend ten to another. Sometimes it's easier rather than just passing down lots of props. So yeah, let's have a look at some custom Dom events. So it's super easy. All you have to do is let's say I have defined an event called as my event. You subscribe to this event like any other event, like adding listener maybe to the document, to the element, whatsoever you feel comfortable with and how to trigger this event, how to fire this event. So you have to create a new custom event with your name and you can pass the data, whatever is required for you. For example, I pass is clicked. And when this custom event is ready, all you need to do is dispatch this event. So this dispatch event will make it available for all the subscriber in the window. So it has nothing to do with microfrontend, app shell or anything. It is plain native JavaScript. So everything which ends in the browser is JavaScript, HTML, CSS. So it doesn't matter whichever microfrontend you are, whichever app shell you are, if an event is fired and it has a subscriber, the subscriber will get the event. So based on that logic, we build this whole messaging system using custom dome events. And that works pretty good out of the box solution for communication. Now we have seen the architecture of the microfundance. Now let's see how we implemented this one. So there were several ways we tried to implement the microfrontend architecture. Initially what we did is like we have small components and then we exported them as node modules and imported them into the projects. This way worked for a while, but still it blocked our deployment because eventually at end of the day, you have to deploy these node modules with the incremental version into the main app. So we are still at the same problem, but with webpack five we have module Federation. So module Federation allows webpack to reference some modules which are not present at the compile time and they can be available at the runtime. So let's have a look at this again. So when we compile host, we do not need to have remote one, remote two, remote three. We just pass the reference of remote one, remote two, remote three with help of module federation plugin and assume that these will be these when the application will be up and running. So this allows to compile the host without any external remotes. And remote one, remote two, remote three are compiled separately and ready for consumption. So on the runtime when the app is up, it looks for the remote one, and when it gets the packages it just chunk in into the host compiled code and behaves like any other component. Now let's have a look at some code. So consider this main JSX. It's a simple react app. It is just a component rendering h three with a title as a prop. So we need to expose this component into these wild. So how would we do that? So it's pretty simple. This is our remote config. This is basically webpack config. And in this webpack config the first thing we need to do is include module federation plugin. So this is native webpack plugin which comes with webpack five. So it has first entry as remote one, the name. So this is the namespace with which it will be known into the host. The second one is the file name remote entry. So remote entry is a file which is created with the model federation. So consider this file as a metadata file. It contains all the address, it contains all the address and the package, and the relation between these packages when which package has to be loaded. And then we have this exposes. So this is these place where we define which component we have to expose. For us it's src main JSx and with which namespace it will be exposed. So it's main. And the final thing which we have is shared. So what module federation allows is like if you are in the same ecosystem, let's say everywhere you are using react. So you should not load two copies of react into your app. So these shared key allows you to define what all libraries you expect to be provided from the host. So in our case we say react and react dome, please use it from host and do not load a copy of it from micro frontend. So with this the module is already exported. So now this exposed module has to be consumed and let's see how we will do that. So again this is the host config of webpack. So again here we have to not write exactly here we have to include module Federation plugin and give a namespace, host namespace. And then we have to define the remotes. So we need to define like what all remotes will be available. So let's say we define the remote one and its address these it can pick up the remote entry js, the entry file which will kind of explain the rest of the things. And these finally again, the shared so as I explained before, we can define some modules which can be not modules, libraries, basically vendor modules which can be shared from host to all the micro front ends. So with this, the connection has already been made between the micro frontend and the host. So this host will consume the micro frontend remote one which will be available at localhost 3002 and having remote entry on that address. Now the connection has been made, but still we haven't used the component. So let's check how to use that main component. It's as simple as this. It's literally like this. If you look at the second line import remote app from remote one main. So remote one is the namespace of the exposed remote and main is the namespace of the exposed component. And then remote app can be used as any other react component throughout your app. So you can pass the props to it, you can render it, you can conditional render it, whatsoever you want to do with it and with the simple steps. You're already having microfundance setup running. So I have prepared a small demo and let's have a look at it. So these I have two projects, host and remote. In remote it's a simple react setup with a webpack config. In the webpack config we have module federation plugin with namespace of remote one remote entry and exposes a shared component which is present in its source folder. And in addition it expects some shared libraries like React and react dome from the host. Let's have a look at the shared component. The shared component is just h four rendering current count which is counter these value passed from the props. Let's have a look at these remote app it's a simple app, remote app, it has a shared component and the chunk value here is just one static one. Now let's have a look at the host in the host in the webpack config. Again we have model federation plugin. It's a host namespace and it accepts a remote remote one at the address localhost 3002. And it exposes some shared libraries like React and React dome. And now let's have a look at host app. So host app basically imports react component remote component from remote one namespace from remote one namespace, and shared component namespace which was exposed. And this, it simply uses it as a component and pass a counter to it. This counter is a state variable and on a button click, on a button click, it increases the counter by one. So this is basically a functional component and it's passing state to these remote component. So let's see how this works in terminal, sorry, in browser. So let's make it run. Let's run the remote first and then let's run the host. So this is on localhost 3002 and this is on localhost 3001. Let's have a look at both. It's, let's have a look at the remote first in remote. If you can see it's a simple remote app with current count one. So the inner box is the shared component which is available in the remote app. Now let's check our host app at 3001. Here again we have the same component, shared component, but it is being served from the remote. Let's quickly have a look at the network and just reload it. And if we see we have a remote entry, main JS, which is initiated by main js and then remote entry in turn invokes lots of modules here, like for example shared component which we need. And let's check the functionality of this. We increase the counter one by one. So the upper one, the count in host is five and current count in shared component is five. So basically it's seamlessly forwarding the state from host app to the shared component. And this is the magic of model Federation. It really seems out of the box, just same native react component as if it was present in the scope of this host project. So with this we have lots of power from module Federation to make sure our react components still work the same way, even if it is not included in the project. So let's get back to our slides. Okay, so we have implemented microfrontend and investing in in our shop, but it was not piece of cake. We have a bit of challenges while developing this micro frontend, so I want to share some of our challenges with you. So first one was design consistency. When we were splitting out micro front ends, one of the major concern of us was like how to keep the design consistent throughout the micro frontend. Right now we have a conscious like okay, we will do these, but when the team grows, when the code grows, how will we make sure that the design is consistent throughout all the micro front ends? So what we came up with was a design system. We have something called, we call has UI kit. UI Kit is basically house of all the components which are available for the UI, for example buttons, search bar, drop downs, checkbox, etc. So whatever UI component we have, it should be in the UI kit and then every micro frontend should use it from the UI kit instead of implementing of their own, even if they want to implement their own. First we implement that in UI kit and then we consume from there. And we have to make a small storybook for this one so that everyone knows what elements are available in the UI kit. And this actually helps the new developers and also the designers to know what we have and so that these can infer from our design system. The next challenge we had was initializing a new micro front end. With each micro front end we have lots of setup, we have GitLab pipelines, we have CI setup, we have Docker setup, we have helm charts, we have publishing to s three scripts, and a lot of stuff on the infra side. So doing this manually is pretty kind of extensive work and also very error prone. So instead of doing it manually for every micro frontend, what we use is a templating engine. We call it temporeto. So temporato is very smart templating engine. It maintains different templates for us, and with the help of these complete, it spins up a new micro frontend or whatever your project is within a minute. So if we do something like this, if you can see on my screen, so these template create it, reuse a template project where all the templates are present and we have several templates, but for this we are interested in micro frontend template. So when we select micro frontend template and go ahead, we pass some variables. These variables are basically kind of namespaces which can be kind of find and replace while creating the template. So once the template is created out of the box we have, as you can see, docker file, helm charts, CI pipelines, end to end test, everything set up already. One more advantage of using this template engine for us is we have lots of micro front ends and we need to make sure that all the micro front ends are in sync on the infra level. For example, if we change the, let's say s three script, how we publish it, we change some stuff there. So we need to forward it to every micro front end. So instead of doing it that manually, we just update the template and micro front ends update their part of these template and it propagates uniformly throughout the micro front ends. So using a template really kind of eased our lives as a developer. Apart from these, we have some more challenges for example, the biggest one was decoupling code from app shell. Okay, so what we did is when we decided to move to micro frontend, we said what we have this monolith, we will call this app shell. Instead of creating a new app shell, we will have this as an app shell. And we will be taking out components one by one, so that our app shell will be leaner. And finally we will having only header and footer and some business logic in app shell and rest, everything will be a micro frontend. So to achieve that, the first thing we did was moving components to the design system. So every UI component, we moved into the design system. And once we have in the design system, every reference of that was only from UI kit. There was no reference, internal reference from one place to another. In the code made be microfrontend, made be Appshell, uniformly. Anything which is related to UI has to be in UI kit and it has to be referenced and used from there itself. So doing this actually kind of half double work, because this enables us to decouple lots of stuff already, even in the app shell. Now sharing the logic between microfrontends, next thing which we want to tackle was some logic which is static, it does not require data, but for example price formatters. So we want our website to have the same price formatting throughout the website. Like maybe any micro frontend may be any page, we want it same. So instead of copying this logic into every micro front end, we created some small utility NPM packages, like price formatting helpers or some date formatting helpers. So these are small helpers which we use throughout our micro frontend system. So whenever we find a utility which is shared by more than two micro front ends, we create a small package out of it. And this logic is used from the packages rather than just existing it twice or twice. So this kind of still makes sure that our code is consistent and we are not kind of using different logic at different parts of our website, which is eventually a different micro frontend. And last but not the least, building an efficient developer experience. So once we have all these micro front ends ready, the biggest problem we had was like, let's say we have one app shell and three micro front ends. To develop it locally, we have to run all four together. So on 3001, two, three, four, we were running micro front ends and the app shell, and then we were able to make some change. And this was pretty cumbersome process because it takes lots of resources. My laptop fan was really like I'm doing a coin mining or something. But eventually we get over that. So in order to fix this, what we did is we followed a docker based approach. So we created a docker image of everything which is deployed on staging, and we accepted the macro front ends URL via environment variable in this docker image. So if there is no environment variable present, we use the staging URL, else the environment variable. So when we develop on the local system, we run, let's say on localhost, three housed and one the micro frontend, and pass it into the docker image with an environment variable. So when we run the docker image, everything is used from the staging environment but the micro frontend from the local environment. So this helped us to have a smooth and more productive developer experience. There are still things which can be improved in this, but for now it's way better than running four node processes. So yeah, this is kind of a snapshot, what we did at Westwing and how we were solving the problems and how we broke our huge monolith into small micro front ends and app shell. Still, we have a long way to go, but from past six months, the progress we have, I can totally say this is super worth it with that. Thank you everyone. Thanks for attending my talk.

Trishul Goel

Principal Engineer @ Westwing

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